1. Technical Field
This disclosure relates to a method of manufacturing a charge-trapping dielectric and a method of manufacturing a silicon-oxide-nitride-oxide-silicon (SONOS)-type non-volatile semiconductor device. More particularly, this disclosure relates to a method of manufacturing a charge-trapping dielectric including a silicon-rich nitride thin film and a method of manufacturing a SONOS-type non-volatile semiconductor device using the charge-trapping dielectric including the silicon-rich nitride thin film.
2. Description of the Related Art
In general, a non-volatile semiconductor device can be classified as either a floating gate type non-volatile semiconductor device or a floating trap type non-volatile semiconductor device. Particularly, the floating trap type non-volatile semiconductor device includes a silicon-oxide-nitride-oxide-silicon (SONOS)-type non-volatile semiconductor device.
The floating gate type non-volatile semiconductor device includes a tunnel oxide layer, a floating gate, a dielectric layer, and a control gate formed on a semiconductor substrate in a unit cell. The floating gate type non-volatile semiconductor device stores charges, which serve as free carriers, in the floating gate. If the tunnel oxide layer disposed between the floating gate and the semiconductor substrate has defects, all the charges stored in the floating gate may be lost. Thus, the tunnel oxide layer is relatively thick to prevent the charges from being lost from the tunnel oxide layer. However, a high operating voltage is needed for the above relatively thick layer, so that circuit compositions for applying the high operating voltage may become complicated. Therefore, the floating gate type non-volatile semiconductor device has limits with respect to the degree of integration.
The SONOS-type non-volatile semiconductor device includes a charge-trapping dielectric and a single electrode formed on the charge-trapping dielectric in a unit cell. The charge-trapping dielectric has a multilayer structure in which a first silicon oxide, a silicon nitride layer, and a second silicon oxide layer are formed. The SONOS-type non-volatile semiconductor device performs programming by a method of storing electrons in a trap formed in the charge-trapping dielectric positioned between the single electrode and the semiconductor substrate. The first silicon oxide layer may be relatively thin because the electrons are stored in a deep-level trap formed in the silicon nitride layer.
When the first silicon oxide layer is relatively thin, the SONOS-type non-volatile semiconductor device may be driven at a low operating voltage so that circuit compositions for applying the operating voltage may be simple. Therefore, the SONOS-type non-volatile semiconductor device has an advantage of having high-integration capability.
An example of the SONOS-type non-volatile semiconductor device is disclosed in U.S. Pat. No. 6,501,681. In the SONOS-type non-volatile semiconductor device, however, when the electrons stored in the silicon nitride layer are erased, the electrons may not be completely erased because the stored electrons do not completely move into the semiconductor substrate during the erasure. Particularly, while erasing the stored electrons, the stored electrons in the silicon nitride layer tunnel through the first silicon oxide layer to move into the semiconductor substrate by a Fowler-Nordheim tunneling process, but electrons created in the single electrode move into the silicon nitride layer through the second silicon oxide layer, so that the electrons may not be completely erased.
Additionally, a method of manufacturing the SONOS-type non-volatile semiconductor device is disclosed in Japanese Patent Laid-Open Publication No. 2002-217317. In the method of manufacturing the SONOS-type non-volatile semiconductor device, a silicon oxide (SiO2) layer, which serves as a lower dielectric layer, is formed on a semiconductor substrate. Sequentially, a silicon nitride layer storing charges is formed on the silicon oxide layer by an atomic layer deposition (ALD) process using silane (SiCl4) gas and hexachlorodisilane (Si2Cl6) gas. An upper dielectric layer and a gate electrode are formed on the silicon nitride layer to complete the SONOS-type non-volatile semiconductor device.
However, in the above-mentioned method of manufacturing the SONOS-type non-volatile semiconductor device, the silicon nitride layer is formed by the ALD process to reduce an incubation time of the silicon nitride layer and improve its interface characteristics. Thus, forming a silicon nitride layer having a high trap density is difficult. Additionally, because the silicon nitride layer is formed while a flow rate of ammonia gas is increased, the SONOS-type non-volatile semiconductor device has limits in being able to improve an erase speed, which is a speed of removing the trapped electrons in the silicon nitride layer. That is, because the silicon nitride layer does not contain silicon-rich nitride, the SONOS-type non-volatile semiconductor device has limits in its ability to improve the erase speed.